This invention relates to a method of allowing or suppressing deployment of an inflatable restraint based on sensed occupant capacitance, and more particularly to a method of taking into account both static and dynamic capacitance data.
Vehicle occupant capacitance sensing systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of characterizing the occupant for purposes of determining whether to allow or suppress deployment of the restraints. For example, it is generally desired to allow deployment for an adult, and to suppress deployment (or reduce deployment force) for a child. However, it has been found that a child occupant can produce a static capacitance reading similar to that of a small adult (5th percentile female) due to variations seat belt tension, the orientation of the occupant on the seat, and the usage of aftermarket seat covers or pads, for example. In other words, the static capacitance readings for a child occupant and a small adult occupant statistically vary over first and second ranges due to system variability, and there can be some amount of overlap between the first and second ranges under certain conditions. Accordingly, what is needed is a method of more reliably distinguishing between those occupants for whom deployment should be suppressed and those for whom deployment should be allowed.
The present invention is directed to all improved method of selectively suppressing deployment of a vehicular inflatable restraint in which both static and dynamic variation in the measured capacitance of a vehicle occupant are used in a complementary manner that reduces overall system variability. The decision to allow or suppress deployment of the restraint is determined based on a comparison of the static capacitance reading with at least one threshold, and the dynamic variation of the measured capacitance and other parameters such as seat belt tension, seat humidity and seat temperature are used to adjust the threshold in a direction to minimize the overall variability of the system. In the preferred embodiment, the variation of the measured capacitance with respect to the variation in vertical acceleration of the vehicle is used to estimate the free capacitance of the occupant, and such free capacitance is used to adjust the threshold.